A model
engine makes sounds that will tell you how it's performing.
You'll have to listen very carefully for them, recognize their
message, and make adjustments to the fuel control needle valves
accordingly. The mixture of fuel and air is controlled by
the amount of fuel metered by the needle valve.
SLOPPY
RICH MIXTURE running is characterized by a very slow,
irregular, sputtering exhaust sound. The exhaust gas will
be very smoky and contain many droplets of oil. This condition
is good for the very first initial run of a ringed or lapped
engine as it receives excess lubrication and runs cooler.
RICH
MIXTURE running is characterized by a slower, sometimes
irregular, sputtering exhaust sound. The exhaust gas will
be smoky and probably contain small droplets of oil. This
condition is good for Break-in since the engine receives excess
lubrication and runs cooler.
FOUR
CYCLING or SLIGHTLY RICH is a rich type setting,
but it is fast enough to pull the airplane. This is the setting
you normally look for before launching the airplane because
the engine will run leaner when airborne.
PEAKED
OR TWO CYCLE. As the main needle is closed (clockwise),
it reduces the amount of fuel mixed with the air drawn into
the engine. At a specific point, which varies with each engine,
air temperature, altitude and relative humidity, the exhaust
note will change quickly into a smooth, powerful note. If
the needle is closed further, the note will stay smooth, but
will weaken. The peak occurs just at the break point from
a rich setting and further leaning will ruin the engine. A
lean setting raises the engine heat above the safe point,
reduces lubrication, and destroys glow plugs due to high combustion
temperature. This is very harmful to the engine and your investment.
Learn to tune the engine before flying. Remember, a little
rich is always preferred for long motor life.
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